For example, vehicular devices are supplied with power by a vehicle battery. In a vehicle, during a cranking of an engine start, a high current flows through an engine starter of the vehicle. Thus, an input voltage, which is provided by the vehicle battery, may decrease to an extremely low voltage, such as 3 volts. Thus, during the cranking, instantaneous interruption may occur to the vehicular devices. It is desirable to supply stable power to the vehicular device even during the cranking.
Regarding above-described difficulty, the vehicular device usually includes a switching power supply device. The switching power supply device switches an operation mode, corresponding to an input voltage, from one power control operation to another power control operation. With this configuration, the switching power supply device stabilizes an output voltage even when the input voltage drastically decreases. For example, as shown in JP H10-243642 A (corresponding to U.S. Pat. No. 5,914,591 A), the switching power supply device switches the operation mode, corresponding to the input voltage, between a buck operation and a boost operation. The switching power supply device further switches the operation mode, corresponding to the input voltage, between two of the buck operation, a buck-boost operation, or the boost operation.
However, during an operation switch from one power control operation to another power control operation, substantially high inrush current flows to one of switching elements included in a switching circuit. The one of the switching elements turns on in order to output the input voltage through the inductor. Thus, during a switch of the power control operation, the output voltage of the switching power supply device may become unstable.